Transposition of the Great Arteries
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Transposition of the great arteries (TGA) is a congenital heart defect where the two main arteries responsible for carrying blood from the heart to the lungs and body are reversed. In this condition, the aorta, which should be connected to the left ventricle, is instead connected to the right ventricle, while the pulmonary artery, which should be connected to the right ventricle, is connected to the left ventricle. This abnormality results in oxygen–poor blood being sent to the body instead of the lungs, and oxygen–rich blood returning to the lungs instead of being distributed throughout the body. Without treatment, babies cannot survive with this condition.
TGA has two types:
- Dextro–transposition of the great arteries (D–TGA) is a medical condition that leads to a reduced supply of oxygen–rich blood to the body. The symptoms of this condition usually become apparent during pregnancy, shortly after birth, or within a few weeks following birth. If left untreated, D–TGA can give rise to severe complications or potentially result in death.
- Levo–transposition of the great arteries (L–TGA) is a relatively rare form of transposition. Its symptoms may not manifest immediately, and the treatment approaches vary depending on the specific heart issues linked to this condition.
One of the common heart defects associated with Transposition of the Great Arteries (TGA) is the presence of a ventricular septal defect (VSD), which refers to an opening in the ventricular septum. The ventricular septum is the wall that separates the two lower chambers of the heart. The presence of a VSD allows for the mixing of oxygen–poor blood and oxygen–rich blood.
The standard treatment for TGA involves surgical intervention to correct the positioning of the arteries. Typically, this surgery is performed shortly after the baby is born.
Symptoms
During a routine pregnancy ultrasound, the condition known as transposition of the great arteries (TGA) can be detected in a baby before birth. However, individuals with the congenitally corrected form of TGA may not exhibit any symptoms for an extended period of time, sometimes spanning many years.
After birth, symptoms of transposition of the great arteries may manifest as follows:
- blue skin color (cyanosis)
- Weak pulse.
- Poor feeding
- Poor weight gain.
When a baby with TGA also has additional heart issues, any changes in skin color may not be immediately apparent due to the presence of other heart problems enabling some oxygen–rich blood flow throughout the body. However, as the baby becomes more active, the blood flow decreases, leading to a more noticeable blue or gray skin color. It is crucial to seek emergency medical assistance if anyone exhibits a blue or gray skin color.
Causes
Transposition of the great arteries can happen during pregnancy as the baby’s heart forms. The exact cause is often unknown.In a normal heart, the pulmonary artery, which carries blood from the heart to the lungs, is connected to the right ventricle, the heart’s lower right chamber. From the lungs, oxygen–rich blood is pumped to the left atrium, the upper left chamber of the heart. It then flows into the lower left chamber, known as the left ventricle. Finally, the body’s main artery, the aorta, is connected to the left ventricle, enabling the pumping of oxygenated blood out of the heart and its distribution to the rest of the body.
Risk factors
There are several factors that can increase the risk of transposition of the great arteries in a baby. These include:
- German measles or another viral infection during pregnancy.
- Consuming alcohol or taking certain medications while pregnant.
- Smoking during pregnancy.
- Poorly controlled diabetes during pregnancy, also known as gestational diabetes.
Diagnosis
Transposition of the great arteries is typically identified after a baby is born, but occasionally it can be detected before birth through a routine pregnancy ultrasound. In such cases, a fetal echocardiogram may be performed to confirm the diagnosis by examining the unborn baby’s heart. After birth, healthcare professionals may consider the possibility of TGA if the baby exhibits symptoms such as bluish or pale skin, a weak pulse, or difficulties with breathing. During a physical examination, the healthcare provider may also detect a heart sound known as a murmur when listening to the baby’s heart.
Confirmation of a diagnosis of transposition of the great arteries may require several tests, including:
- Echocardiogram. This procedure utilizes sound waves to generate dynamic images of the pulsating heart. It visually demonstrates the movement of blood within the heart, including its flow through the heart valves and blood vessels. Additionally, it can provide insight into the locations of the primary arteries exiting the heart. Furthermore, an echocardiogram has the capability to identify congenital heart abnormalities like a cardiac septal defect.
- Chest X–ray. A chest X–ray provides information about the heart and lungs, but it is not sufficient to diagnose TGA. However, it does assist healthcare providers in assessing the size of the heart.
- Electrocardiogram (ECG or EKG). A simple and painless test is used to measure the electrical activity of the heart. The test involves placing sticky patches called electrodes on the chest, and sometimes on the arms and legs. These electrodes are connected to a computer with wires, which displays the results of the test. By examining the results, a doctor can determine if the heart is beating too fast, too slow, or not beating at all.
- Pulse oximetry screening: pulse oximetry screening for newborns is a common procedure used to assess oxygen levels as part of their routine care.
Treatment
Surgical intervention is necessary to correct the heart problem in all infants diagnosed with complete transposition of the great arteries (D–TGA). However, the treatment approach for congenitally corrected transposition (L–TGA) varies depending on the timing of diagnosis and the presence of any additional heart conditions.
Medicines
Before performing surgery to correct the switched arteries, doctors may administer a medication called alprostadil. This medication enhances blood flow and promotes improved mixing of oxygen–poor and oxygen–rich blood.
Surgery
Treatment options for TGA vary depending on the specific type of TGA. While not all individuals with congenitally corrected transposition require surgery, it is typically recommended for most cases. Surgical interventions and other treatments for TGA may include:
- Atrial septostomy: This is a procedure that can be performed as an immediate, short–term solution prior to surgery. It involves the use of slender tubes and small incisions to expand a natural connection between the upper chambers of the heart. This process facilitates the mixing of oxygen–rich and oxygen–poor blood, leading to improved oxygen levels within the baby’s body.
- Arterial switch operation: The arterial switch operation is a frequently performed surgical procedure for correcting transposition of the great arteries, which is a common congenital heart defect. In this surgery, the two primary arteries that exit the heart are repositioned to their appropriate locations. Other heart problems present at birth may be repaired during this surgery.
- Atrial switch operation: During the surgery, the surgeon divides the blood flow between the two upper chambers of the heart. As a result, the right lower chamber of the heart now needs to pump blood not only to the lungs but also to the rest of the body.
- Rastelli procedure: In some cases, when a baby has a heart condition called TGA and also has a hole in the heart known as a ventricular septal defect, a surgery may be performed. During this surgery, the surgeon closes the hole and changes the way blood flows in the heart. This allows oxygen–rich blood to reach the body. They use an artificial valve to connect one part of the heart to an artery leading to the lungs.
- Double switch procedure: The goal of the surgery is to change the way blood flows into the heart. By rearranging the connections of the major arteries, the surgery allows the lower left chamber of the heart to pump oxygen–rich blood to the body’s main artery, called the aorta.
- Pacemaker: If TGA produces slow heartbeats, a pacemaker device may be advised. This is usually associated with the closure of the VSD.
